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Old 14th November 2012, 12:59 AM   #7561
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Unfortunately, MOST regulated supplies are current limited, AND they cannot supply the transient current so loved by Otala and me, as well. That is why I don't usually use regulated power supplies in my Parasound power amps. Just regulation in the DRIVER supplies.
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Old 14th November 2012, 01:40 AM   #7562
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input/drive circuit PS filtering, cascodes, referencing compensation to AC gnd instead of a supply are all good

but I did enjoy Self's argument on power amp output Q supply regulation - when asked for it in a new design assignment he replied by asking what was the logical improvement vs putting hard clipping on the input
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Old 14th November 2012, 01:51 AM   #7563
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To my taste, it's not the voiltage stabilizers' job to supply transient currents. Capacitors do that better.
Regulated supplies have to be current limited. I remember Soviet amps "Trembita" in which transistors in power supplies did harakiri.
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Old 14th November 2012, 04:54 AM   #7564
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There are techniques for paralleling any number of reasonably low cost pass transistors, or equivalents, as necessary to meet the peak current demand, while minimising the dissipated energy, so this should not be used as an excuse. Again, intelligent engineering can come to the rescue ...

Frank
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Old 14th November 2012, 07:10 AM   #7565
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This 'current spec' is product promotion gone wild! '-)
Completely agreed!
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Old 14th November 2012, 07:17 AM   #7566
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And beyond that, how ensuring that the power supply side of things is thoroughly clean in all senses makes all the difference. I've been laughed at a few times for "claiming" that a lowly 20W chip amp can sound very, very impressive if you do all the right things, but I certainly know what's achievable ...

Only a few months ago I did the rounds of listening to a large range of pro, powered monitors from the best names in the industry and to sum it up they were a joke: I was pushing them all hard, overload led indicators flashing continuously and they still sounded pretty gutless. A key reason for this is the lousy, conventional power supplies used ...

Frank
Although I've never worked with any power chip, I agree with you, Frank. I do so because of two things.

One of the most sensible and meaningful ways of upgrading almost any equipment, and especially the budget sector products, is to upgrade their filter capacitors. Since 1980, I have not heard a single product which was not improved by better qualiy, bigger capacitors; some more, some less, but all sounded better. Should you do a bit more than just the filter caps, such as upgrading the rectification with some fast diodes, and perhaps substituing the usually tight power transformer with something a bit more relaxed, even lowly budget sector amps start to sound serious.

Another reason is that again, I have never yet encountered a power amplifier which did not sound better when its VAS was fed off its own, separate regulated power supplies. Again, some more, some less, but all tend to do from better to much better.
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Old 14th November 2012, 07:30 AM   #7567
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I am now slowly wrapping up my power amp project, and have come to the last, but by no means the least section, the power supply.

I'd like to hear your comments on what I have in mind.

The first thing I am set on doing is slightly spreading arund the filter caps. So, instead of putting all power amp filters on one board, I intend to put 2 10,000 uF caps on their own board, but also a 4,700 uF cap (same model, same manufacturer) on the actual power amp board, followed by 100 uF and 0.1 uF caps. It seems to me it's practical to have it as near the output stage as possible. Views? Opinions? Experience?

The voltage gain stage will be fully regulated, as I have been doing since the early 80ies. The questions which now arise are:

1. Should these regulated lines also feed the predriver only, or predriver AND driver, leaving only the output section to run off capacior fed lines?

2. Or should I go for full voltage/current regulation of the power section as well, separately from what precedes it?

Remember, I am very flexible. It can be a single case stereo amp, or two separate monoblocks, meaning PCB real estate is very flexible.

I am not bound by any price constraints, this is for me and my pleasure, so cost is relatively unimportant.

I have a relative abundance of serious power devices (all by Motorola/ON Semi, MJ 21195/21196 TO-3 250W devices, MJL 3281/1302 plastic pack 200W devices), so there's no problem in using 2, 3 or 4 pairs of power devices, on a separate hefty heat sink.

So, I plan to use 3 or 4 pairs of output devices in the audio section, and it's not a problem to use exactly the same number and type of devices in the regulator, because remember, I do want it to be capable of some rather serious current peaks.

All ideas and views invited.
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Old 14th November 2012, 08:07 AM   #7568
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Has anyone a good current feedback power amp circuit to show ? One that has been is regular use . I have had half hearted attempts to build things . To be honest I doubt what I did was a good version . Not even sure they were correct ?
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Old 14th November 2012, 10:33 AM   #7569
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Quote:
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I am now slowly wrapping up my power amp project, and have come to the last, but by no means the least section, the power supply.

I'd like to hear your comments on what I have in mind.
Where to start ...?!

In summary, a Yes to all your questions! I'm of a mind now where the power supply is the most important part of the amplifier, the amplifying topology is almost a by-the-way! In order of sensitivity to power supply fluctuations, typically the output stage is the least affected, the VAS the most sensitive, which as you say you've addressed before. So add regulation with those priorities in mind; in my experience every effort you make to improve the power supply, in every area, will be rewarded many times over. And be very particular in the routing of power lines or traces so that current pulses do not impact where they shouldn't.

I would read up every tip and thread about optimising power supplies, the important things have been said many times over, and the gains from doing it right can be tremendous ...

Frank
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Old 14th November 2012, 11:48 AM   #7570
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Where to start ...?!

In summary, a Yes to all your questions! I'm of a mind now where the power supply is the most important part of the amplifier, the amplifying topology is almost a by-the-way! In order of sensitivity to power supply fluctuations, typically the output stage is the least affected, the VAS the most sensitive, which as you say you've addressed before. So add regulation with those priorities in mind; in my experience every effort you make to improve the power supply, in every area, will be rewarded many times over. And be very particular in the routing of power lines or traces so that current pulses do not impact where they shouldn't.

I would read up every tip and thread about optimising power supplies, the important things have been said many times over, and the gains from doing it right can be tremendous ...

Frank
Thank you, Frank, we seem to agree across the board.

I also think it's very difficult to overdo it with power supplies.

A few weeks ago, I took out some 20+ year old 6,800 uF caps out of a Toshiba integrated amp and soldered a pair of 10,000 uF brand new caps, nicely formed. Bearing in mind that the old gave place to the new, in itself a leap forward, the extra 47% of capacitance did wonders for the unit. I would have gone even further, but there was no more space left for still bigger caps.

And that's strictly a low level, budget amp from 1982, delivering a nominal 50WRMS into 8 Ohms, using 80W SEPP output stages. I should add that I was VERY surprised at the way it was constructed, I would never have thought it possible to use such circuitry in such a budget model, belying its price grade and far belying its perceived level of technology. Then again, Toshiba does make all those components.

I understood it as an object lesson - serious people will be serious at any price level.

And it made me promise myself to throw away my wallet when it comes to power supplies.
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